Aliens of the Abyss – Feeding in Goblin Sharks

Goblin sharks (Mitsukurina owstoni) are an extremely unique species of shark and have a very unusual appearance. They possess a prominent snout that protrudes from the top of the shark’s head, this snout is long and flat, resembling the blade of a sword. Goblin sharks are often referred to as “living fossils” as

their ancestry goes all the way back to during the cretaceous period, around 125-113 million years ago. The skin of the Goblin shark is semi-translucent and covered with dermal denticles, with their pinkish colouration produced by oxygenated blood flowing through blood vessels just beneath the surface of the skin. They are not overly large sharks, with adults ranging in length from 3-4 metres.

Habitat

Goblin sharks are found globally in all major seas, the greatest frequency of sightings being around the waters of Japan, but have a non-uniform distribution. Sightings of these sharks are very rare as they usually inhabit great depths, with adult Goblin sharks being found at depths of 1,300 to 1,400 metres. They are bottom dwelling sharks, inhabiting upper continental slopes, submarine canyons and seamounts however they have been found in shallower waters at depths as shallow as 40 metres. Unlike the adults, juveniles are found in shallower depths of around 100-350 metres.

Feeding

The environment that Goblin sharks inhabit is harsh and nutrient poor which is reflected somewhat by the body of the shark. The major muscle blocks of the shark are soft and very weak, and the bones of the shark are poorly calcified. This is likely a result of a nutrient poor diet. When combined with the shark’s small soft fins all these factors point to the fact that the Goblin shark is not a fast swimmer and exhibits a lethargic

lifestyle. Their low-density flesh and a large oily liver result in the shark being neutrally buoyant, allowing the shark to drift towards prey with minimal movement to avoid detection. This suggests that the Goblin shark is more of an ambush predator. Stomach contents of Goblin sharks that have been examined reveal a diet of mainly teleost fish, while also feeding on organisms such as squid, crabs and other cephalopod species.

Detection

The main detection method used by the Goblin shark to locate prey is electroreception. The snout protruding from the top of the shark’s head is covered in jelly filled pores known as the Ampullae of Lorenzini. These pores sense even the most minute of electromagnetic fields emitted by living organisms. The sharks will sweep their snout back and forth over the seabed in order to detect prey organisms hiding there and will also use the snout to disturb the sandy bottom. Whilst the eyes of the Goblin shark are small and are not overly relied upon for prey detection it is believed that they are used in combination with the Ampullae of Lorenzini to effectively locate prey.

Lightning strike

The large parabolic shaped jaws of the Goblin shark are arguably its most defining characteristic. The jaws are protrusive and are the key part of the Goblin shark’s hunting technique. As soon as any unfortunate prey organism enters striking distance, the jaws of the Goblin shark snap forward like a catapult, rapidly engulfing and capturing the prey. The jaws move at speeds as quick as 3.1 metres per second, which is faster

than most Cobra strikes. When combined with the fact that the jaws can extend to the end of the snout the Goblin shark has an impressive strike range with which to capture prey. The rapid forward thrust of the jaw is provided by a pair of elastic ligaments connected to the shark’s mandibular joint, these ligaments are pulled tight and tensed whilst the shark’s jaw is closed. Whilst swimming the ligaments hold the jaws of the shark tight. However, once it is time for the shark to bite the ligaments holding the jaw in place relax, using the tension that the jaw is under to catapult it forward and towards the shark’s prey. As the jaw opens, water is sucked into the shark’s mouth and dragging the prey with it. There is also a significant amount of tooth variation within the jaw. Goblin sharks possess 35-53 rows of upper teeth and 31-62 rows of lower teeth. The size of these teeth varies throughout the jaw, with the teeth at the back of the jaw being smaller and flattened for crushing and the teeth towards the symphysis (jaw midpoint) being longer for gripping prey.

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